The present invention relates to an epitaxial reactor for chemical vapour deposition (CVD), of the kind using an induction heated susceptor, implemented in two discrete reaction chambers alternatively actuated by some power AC generator, preferably but not limited to medium frequency power generators.
It is well known to use epitaxial reactors for CVD deposition of layers on single crystal wafers, specially in the field of semiconductors (Si, GaAs or the like), for producing complex components.
In the above mentioned field the nowadays problem of cost reduction is more and more pressing. The cycle of the CVD deposition consists of the following steps:
Loading step of products (one or more wafers);
Purge step by means of inert and/or reducing gas such as, for example, N2, H2;
Heating up step to increase the temperature from loading to deposition temperature;
Deposition step;
Cooling down step to decrease the temperature from deposition to unloading temperature;
Purge step by means of reducing and/or inert gas such as, for example, H2, N2; and
Unloading step of products (one or more wafers).
The productivity, or production rate in a time unit, of an epitaxial reactor can be increased by affecting both the above single steps and the whole assembly thereof, for example by either increasing the number of reaction chambers contained in a single reactor or increasing the batch load.
In fact, the cost of every epitaxial wafer is affected by some parameters, the most important being:
1. The direct cost of used gas, electric power, materials, etc.;
2. The amortization or redemption share for every produced wafer;
3. The productivity for every surface area unit, i.e. the necessary investment cost for installing every epitaxial reactor.
It is an object of the present invention to reduce the costs connected to the above parameters 2 and 3.
The subject matter of the present invention is an epitaxial reactor, consisting of two reaction chambers, or stations, mounted on a single support frame, induction heated by a dual output medium frequency generator, wherein just one reaction chamber at a time can be operated while the other one has to carry out purge, loading and unloading steps, having however an overlap between the operating times of the two stations lasting till 20 minutes.
Also the only fact of being provided with two reaction chambers, instead of one, allows to increase the productivity. In fact, a reactor having two stations allows a productivity increase ranging from a minimum of 35% to a maximum of 100% with respect to a reactor having the same features, but just one station and a reaction chamber alone.
The 35 to 100% range is connected to the layer thickness to be deposited, i.e. to the time duration of the deposition step. When the steps of heating up, deposition, cooling down (the last step is taken into account only if the generator has been actuated) have a time duration shorter than or equal to that of the purge, loading/unloading steps, the productivity gain goes to 100%. The solution with two reaction chambers in just one reactor is intrinsically more efficient than the solution with just one reaction chamber.
An alternative approach consists in mounting two completely independent reaction chambers inside a reactor.
Such an approach allows an higher productivity but at price of a higher complication. In fact, requires the presence of two medium frequency generators, a more complex gas control board and generally the doubling of the basic functions. The installation of such a reactor is indeed more complex and, above all, outstandingly expensive. In the here below enclosed Table 1 the productivities or production rates are listed for:
a reactor having just one station and one power generator;
a reactor having two stations and two alternatively actuated power generators, the on time (operating time) of one generator coinciding with the off time (rest time) of the other generator (traditional prior art);
a reactor having two stations and two alternatively actuated generators, according to a design of the present invention, with an overlapping in the operating times of the two stations; and
a reactor having two simultaneously working stations with independently actuated generators (case conventionally called xe2x80x9ctwo reactors in onexe2x80x9d).
The present invention consists of using a medium frequency generator, having the same layout of a traditional generator, but with two independent power outputs, every output being connected to a reaction chamber.
The invention allows not to overburden the installation conditions and not to uselessly complicate the reactor which do not show any further change with respect to the standard reactors.
Substantially, the invention allows, in a reactor comprising two stations or reaction chambers, to either partially or totally overlap the heating up time of the waiting station to the reaction or deposition time of the station performing the process. According to a preferred embodiment of the invention, such an overlap is of 10 minutes, meaning that 10 minutes before the end of the deposition step in the reaction chamber under process (or, more generally, 10 minutes before the end of the working time of the generator for that reaction chamber) power is supplied to the other station (on the related output of the generator) so beginning the heating up step 10 minutes in advance with respect to the traditional process.
Of course, the 10 minute overlap is just an example coinciding this time with the whole time of the heating up step ranging from 1 to 20 minutes, as it is well known in the art. (see for example U.S. Pat. No. 5,037,674 for chemical deposition of GaAs films).
As in the heating up step is expected only the use of inert gas, changes in the gas supply board, already arranged for the simultaneous purge of two reaction chambers, are not required.
More in general no hardware modifications are required, with no increase of the reactor complexity.
The productivity increase depends on the layer thickness but it is at least 20 to 30% of the productivity of the reactor having two stations with a traditional power generator.